Method for forming field effect transistors

ABSTRACT

A method for forming field effect transistors comprises forming a first dummy gate stack over a first fin, forming a second dummy gate stack over a second fin, depositing a first layer of spacer material on the first dummy gate stack, the first fin, the second dummy gate stack, and the second fin, patterning a first masking layer on the first dummy gate stack and the first fin, etching to remove portions of the first layer of spacer material and form a spacer adjacent to the second dummy gate stack, removing the first masking layer, epitaxially growing a silicon material on the second fin, depositing a layer of oxide material on the first layer of spacer material, the first epitaxial material and the second dummy gate stack, and depositing a second layer of spacer material on the layer of oxide material.

PRIORITY

This application is a continuation of and claims priority from U.S.patent application Ser. No. 15/085,376, filed on Mar. 30, 2016, entitled“FIELD EFFECT TRANSISTOR DEVICE SPACERS”, which claims priority fromU.S. patent application Ser. No. 14/817,504, filed on Aug. 4, 2015,entitled “FIELD EFFECT TRANSISTOR DEVICE SPACERS”, each application isincorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to field effect transistors (FET), andmore specifically, to finFET devices.

FinFET devices typically include semiconductor fins that are arranged ona substrate. Gate stacks are arranged on the fins and define channelregions of the device. The source and drain active regions of the deviceare adjacent to the channel region.

In fabrication, sacrificial dummy gate stacks are often formed prior toforming the active regions of the device. The dummy gate stacks definethe channel region, and are formed from a material such as polysilicon.A material such as nitride or oxide is often used to form spacersadjacent to the gate stacks. The dummy gate stacks allow fabricationprocesses such as ion implantation and annealing or epitaxial growthprocess to be performed prior to forming the gate stacks. Such hightemperature processes can undesirably degrade the materials in the gatestacks, thus the dummy gate is used to define and protect the channelregion while the active regions are formed.

Often a wafer includes nFET and pFET devices. The devices aredistinguished by the type of materials in the active regions of thedevices. The active regions may be formed by ion implantation and/orepitaxially growing doped silicon materials.

SUMMARY

According to one embodiment of the present invention, a method forforming field effect transistors comprises forming a first dummy gatestack over a first fin, forming a second dummy gate stack over a secondfin, depositing a first layer of spacer material on the first dummy gatestack, the first fin, the second dummy gate stack, and the second fin,patterning a first masking layer on the first dummy gate stack and thefirst fin, etching to remove portions of the first layer of spacermaterial and form a spacer adjacent to the second dummy gate stack,removing the first masking layer, epitaxially growing a silicon materialon the second fin, depositing a layer of oxide material on the firstlayer of spacer material, the first epitaxial material and the seconddummy gate stack, and depositing a second layer of spacer material onthe layer of oxide material.

According to another embodiment of the present invention, a method forforming spacers of a field effect transistor comprises patterning afirst fin, forming a first dummy gate stack on the first fin, forming afirst layer of spacer material on the first fin and the first dummy gatestack, removing portions of the first layer of spacer material to definea spacer adjacent to the first dummy gate stack, epitaxially growing asilicon material on exposed portions of the first fin, forming a layerof oxide material on the silicon material, the spacer, and the dummygate stack, and forming a second layer of spacer material on the oxidelayer.

According to yet another embodiment of the present invention, a fieldeffect transistor device comprises a first semiconductor fin arranged ona substrate, the first semiconductor fin is doped with n-type dopants, asecond semiconductor fin arranged on the substrate, the secondsemiconductor fin is doped with p-type dopants, a first gate stackarranged over the first semiconductor fin, a second gate stack arrangedover the second semiconductor fin, a first spacer arranged adjacent tothe first gate stack, the first spacer having a substantially uniformthickness, and a second spacer arranged adjacent to the second gatestack, the second spacer having a substantially uniform thickness,wherein the thickness of the first spacer is substantially similar tothe thickness of the second spacer.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with theadvantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 illustrates a cross sectional view of a two finFET devices.

FIG. 2 illustrates a side cut-away view of fins formed on a substrate.

FIG. 3 illustrates the resultant structure following the patterning anddeposition of a masking layer.

FIG. 4 illustrates the resultant structure following the removal of themasking layer and an epitaxial growth process.

FIG. 5 illustrates the deposition of an oxide layer.

FIG. 6 illustrates the deposition of a second layer of spacer material.

FIG. 7 illustrates the patterning of a mask layer.

FIG. 8 illustrates the resultant structure following an etching process.

FIG. 9 illustrates the resultant structure following an etching process.

FIG. 10 illustrates the formation of spacers.

FIG. 11 illustrates the formation of source and drain regions.

FIG. 12 illustrates the patterning of a masking layer.

FIG. 13 illustrates the removal of the masking layer.

FIG. 14 illustrates the resultant structure following the deposition ofan insulating layer.

FIG. 15 illustrates the resultant structure after a planarizing process.

DETAILED DESCRIPTION

The formation of nFET and pFET devices on a single wafer often includesforming the active regions of the nFET devices and the pFET devices inseparate fabrication steps to allow the formation of active regionshaving different types of dopant materials. For example, when the activeregions of the nFET devices are being formed, the pFET devices areprotected by a layer of material that prevents exposure of the pFET tothe nFET active region fabrication process. Likewise, when the activeregions of the pFET devices are being fabricated, the nFET devices areprotected to prevent contamination of the nFET devices. This processoften results in asymmetric pFET and nFET spacers that affect theperformance of the devices. The embodiments described below provide forsymmetrical spacers in pFET and nFET devices formed on a substrate.

FIG. 1 illustrates a cross sectional view of two finFET devices havingfins 102 a and 102 b and dummy gate stacks 104 a and 104 b. A layer ofspacer material 106 a and 106 b is deposited over the devices and formedinto spacers. A second layer of spacer material 108 is formed over thedevices. In the illustrated example, the active region of the fin 102 bhas been formed by an epitaxial growth that was performed prior to thedeposition of the second layer of spacer material 108, while the spacer108 a was formed prior to the epitaxial growth on the fin 102 a. Theresulting structure includes finFET devices having asymmetrical spacers108 where the spacer material 108 at the base of the gate stack 104 a inregion 101 a has a greater thickness than the spacer material at thebase of the gate stack 104 b in region 101 b. When NFET and PFET havedifferent spacer thickness (asymmetrical spacers), forming balancedjunctions for good device behavior becomes difficult. Unbalancedjunctions may either cause higher external resistance or may shortchannel control. The thickness of the spacers also affects the contactarea, and thus, it is desirable to minimize the spacer thickness.

FIGS. 2-15 illustrate an exemplary method of forming symmetrical spacersfor nFET and pFET fin FET devices on a wafer. FIG. 2 illustrates a sidecut-away view of fins 204 a and 204 b are formed on a substrate 202using, for example, a photolithographic patterning and etching methodsuch as reactive ion etching (RIE). Dummy gate stacks 206 a and 206 bare arranged on the fins 204 a and 204 b respectively. The dummy gatestacks 206 are formed by for example, depositing a layer of polysiliconmaterial or oxide material 208 and an oxide or nitride material 210 overthe layer of polysilicon material 208. The photolithographic patterningand etching process may be used to pattern the dummy gate stacks 206.Following the patterning of the dummy gate stacks 206, a layer of spacermaterial 212 is deposited over the exposed surfaces. In the illustratedembodiment, the spacer material 212 includes a low-k material such as,for example, SiN, SiBCN, SiOCN, or SiOC that may be deposited by, forexample, a chemical vapor deposition (CVD) process.

FIG. 3 illustrates the resultant structure following the patterning anddeposition of a masking layer 302 over the dummy gate stack 206 a andfin 204 a. The masking layer may include, for example, an organicmaterial. After the masking layer 302 is patterned, an anisotropicetching process such as, for example, RIE is performed to form thespacers 304 adjacent to the dummy gate stack 206 b. The etching processremoves a portion of the spacer material 212 to expose portions of thefin 204 b.

FIG. 4 illustrates the resultant structure following the removal of themasking layer 302 (of FIG. 3) and an epitaxial growth process. Themasking layer may be removed by, for example, a plasma ashing process.The epitaxial growth process grows an epitaxial material, such as, forexample, silicon or silicon germanium on exposed silicon surfaces of thefin 204 b to further define source and drain regions (active regions)402. The layer of spacer material 212 over the dummy gate stack 206 aand the fins 204 a protects the silicon material of the fin 204 a fromseeding the epitaxy. In some embodiments, the epitaxially grown materialin the active regions 402 may be in-situ doped with either n-typedopants or p-type dopants during the epitaxial growth process.

FIG. 5 illustrates the deposition of an oxide layer 502 over the exposedportions of the spacer material layer 212, the spacers 304, the activeregions 402, and the dummy gate stacks 206. The oxide layer 502 isrelatively thin approximately 1 to 5 nanometers. The oxide layer 502 isformed using, for example a CVD process.

FIG. 6 illustrates the deposition of a second layer of spacer material602 over the oxide layer 502. The second layer of spacer material 602may include, for example, a nitride material that is deposited by a CVDprocess.

FIG. 7 illustrates the patterning of a mask layer 702. The masking layer702 may be formed by, for example, a lithographic deposition andpatterning process. The mask layer 702 is patterned over the secondlayer of spacer material 602 on the dummy gate stack 206 b, and theactive regions 402.

FIG. 8 illustrates the resultant structure following an etching processsuch as, for example, a chemical wet etching process or a reactive ionetching process that removes the exposed portions of the second layer ofspacer material 602. The etching process is selective to the material inthe oxide layer 502 such that the oxide layer 502 is exposed, but notsubstantially etched.

FIG. 9 illustrates the resultant structure following an etching processsuch as, for example, a diluted hydrofluoric (HF) or a buffered HFetching process. That removes the exposed portions of the oxide layer502. The removal of the exposed portions of the oxide layer 502 exposesa portion of the spacer material layer 212 over the dummy gate stack 602a and the fin 204 a.

FIG. 10 illustrates the formation of spacers 1002 adjacent to the dummygate stack 206 a. The spacers 1002 are formed by an anisotropic etchingprocess such as, for example, RIE that removes the exposed horizontalsurfaces of the layer of spacer material layer 212 (of FIG. 9).

FIG. 11 illustrates the formation of source and drain regions (activeregions) 1102 using, for example, an epitaxial growth process that growsa silicon material on the exposed portions of the fin 204 a. The sourceand drain regions 1102 may be in-situ doped during the epitaxial growthprocess with n-type or p-type dopants. In the illustrated embodiment,the source and drain regions 402 and the source and drain regions 1102are dissimilar. In this regard, in one embodiment, if the regions 402are doped as p-type regions, the regions 1102 are doped as n-typeregions. In an alternate embodiment, if the regions 402 are doped asn-type regions, the regions 1102 may be doped as p-type regions.

FIG. 12 illustrates the patterning of a masking layer 1202 over thesource and drain regions 1102, the dummy gate stack 206 a, and thespacers 1002. The masking layer 1202 may be formed by, for example, alithographic patterning and etching process. Following the patterning ofthe masking layer 1202, an etching process such as, for example, achemical etching process, is performed that removes exposed portions ofthe second layer of spacer material 602 (of FIG. 11). The removal of thesecond layer of spacer material 602 exposes the oxide material 502. Theetching process is selective to the oxide layer 502 such that theetching process does not substantially remove the oxide layer 502material.

FIG. 13 illustrates the removal of the masking layer 1202 to expose thesource and drain region 1102, the spacers 1002 and the dummy gate stack206 a.

FIG. 14 illustrates the resultant structure following the deposition ofan insulating layer 1402 such as, for example an oxide material layer.The insulating layer 1402 may be formed by, for example, a CVD process.The insulating layer 1402 is formed over the source and drain regions1002, the dummy gate stack 206 a, the spacers 1002 and the oxide layer502 that is over the dummy gate stack 206 b, the spacers 304, and thesource and drain regions 402.

FIG. 15 illustrates the resultant structure after a planarizing processsuch as, for example, chemical mechanical polishing (CMP) has beenperformed, which removes a portion of the insulator layer 1402 andexposes the dummy gate stacks 206 a and 206 b (of FIG. 14). The dummygate stacks 206 are removed, and gate stacks 1502 a and 1502 b areformed. The gate stacks 1502 include a dielectric layer 1504 and a gateelectrode layer 1506. The finFET device 1500 a includes the gate stack1502 a, the spacers 1002, and the source and drain regions (activeregions) 1102. The finFET device 1500 b includes the gate stack 1502 b,the spacers 304 and the source and drain regions (active regions) 402.In one exemplary embodiment, the finFET device 1500 a is a pFET typedevice and the finFET device 1500 b is an nFET type device. In alternateexemplary embodiments, the finFET device 1500 a is an nFET type deviceand the finFET device 1500 b is a pFET type device. The finFET devices1500 a and 1500 b have spacers 1002 and 304 that have substantiallysimilar thicknesses (t) for the length of the spacer (i.e., from the topsurface of the gate stacks 1502 to the top of the fins 204 a and 204 b.

The exemplary methods and structures described herein include finFETdevices having different type active regions and spacers havingsubstantially similar thicknesses, which improves the performance of thedevices.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of onemore other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The diagrams depicted herein are just one example. There may be manyvariations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

While the preferred embodiment to the invention had been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

1. A method for forming field effect transistors, the method comprising:forming a first dummy gate stack over a first fin; forming a seconddummy gate stack over a second fin; depositing a first layer of spacermaterial on the first dummy gate stack, the first fin, the second dummygate stack, and the second fin; patterning a first masking layer on thefirst dummy gate stack and the first fin; etching to remove portions ofthe first layer of spacer material and form a spacer adjacent to thesecond dummy gate stack; removing the first masking layer; epitaxiallygrowing a silicon material on the second fin; depositing a layer ofoxide material on the first layer of spacer material, the siliconmaterial and the second dummy gate stack; depositing a second layer ofspacer material on the layer of oxide material; patterning a secondmasking layer over the second dummy gate stack and the second fin;removing exposed portions of the second layer of spacer material;removing exposed portions of the layer of oxide material; etching toremove portions of the first layer of spacer material and form a spaceradjacent to the first dummy gate stack; removing the second maskingmaterial; epitaxially growing a silicon material on the second fin;patterning a third masking layer on the first dummy gate stack and thefirst fin; removing exposed portions of the second layer of spacermaterial; and removing the third masking layer.